The present invention is related to a mechanism for coupling motion of an actuator in axisymmetric devices like modulating proportional valves and is especially useful with regard to piezoelectric actuators. The mechanism uses actuator extension motion to cause translation away from a mechanism mounting plane and thereby enables lifting open of a valve element instead of the usual pushing closed of the valve element. The present inventive Interlace Lifting Mechanism can also be combined with the inventor's Multiflex Coupling, as disclosed in related application Ser. No. 13/794,517, already expressly incorporated by reference, in its entirety, herein, to provide increased stroke. The invention is particularly useful in valves intended for proportional, or modulating, control of fluid delivery within industrial processes making semiconductor devices, pharmaceuticals, or fine chemicals, and many similar fluid delivery systems.
The field of control valves intended for use within automated process control systems is broad and well known. Many proportional control valves have one or more movable elements that may be actively positioned, anywhere between an extreme open condition and an extreme closed condition, to adjust the flow of fluid passing therethrough. Fluid delivery apparatuses intended for manipulating process materials within semiconductor manufacturing equipment usually require attention to maintaining high purity of the delivered reactants and also are typically much smaller than valves used in petrochemical plants, for example. Nonetheless, many different types of powered valve actuators are found in high purity instrumentation and control apparatus such as mass flow controllers. U.S. Pat. No. 4,695,034 issued to Shimizu et al. describes use of a stack of piezoelectric disc elements to effect movement of valve parts in a mass flow controller. U.S. Pat. No. 4,569,504 issued to Doyle describes use of a magnetic solenoid with interleaved magnetic circuit elements. U.S. Pat. No. 5,660,207 issued to Mudd describes use of a heated resistance wire that changes length with temperature to effect valve element movement. U.S. Pat. No. 6,178,996 issued to Suzuki describes use of a pressurized fluid, such as nitrogen gas, in a bellows actuator to control the degree of opening of a diaphragm-operated control valve.
One disadvantage of both magnetic solenoid and thermal expansion type actuators is inherent constant power consumption when controlling valve elements are positioned at an intermediate condition, such as when actively regulating fluid flow. A piezoelectric actuator is effectively a capacitor in an electrical circuit, and therefore does not consume current when an applied voltage is constant. Consequently, typical piezoelectric control valve applications only require low power and avoid the undesirable generation of heat found in electromagnetic actuators. A piezoelectric actuator advantageously may produce substantially more force than a solenoid actuator of comparable size, but achievable strain severely limits the distance a piezoelectric stack can move. Valve power consumption is of particular concern in instrumentation devices such as compact mass flow controllers.
Piezoelectric actuators nearly always are used in a manner wherein applying an activation voltage causes an extensional increase in the stack length (see Shimizu et al. '034 and U.S. Pat. No. 5,094,430 to Shirai et al.). Shimizu et al. increase the available movement by interposing a force transmission member, comprising a plurality of radial lever-arm fingers, between the stack of piezoelectric disc elements and the moving portion of the control valve. These force transmission members are complicated and difficult to manufacture correctly. Piezoelectric actuators are typically associated with normally open valves wherein increasing applied voltage then causes the valve to decrease fluid flow. Normally closed valves using piezoelectric actuators, wherein increasing applied voltage then causes the valve to increase fluid flow, often have a complicated fluid flow path structure with a poppet driven by a shaft passing through the valve seat orifice (e.g. see FIG. 3 and FIG. 10 of Shimizu et al. '034) which may adversely impact fluid purity. A valve designer will benefit from having a mechanism to seemingly reverse the direction of actuator extension motion which thereby allows normally closed valves to use a piezoelectric actuator lifting a diaphragm to open the valve while avoiding the complexities and compromises of a shaft through the valve seat.